trap

, onintr

- shell built-in functions to respond to (hardware) signals

Synopsis

sh

trap [argumentn [n2]...]

csh

onintr [-|label]

ksh

*trap [argsig [sig2...]]

Description

sh

The trap command argument is to be read and executed when the
shell receives numeric or symbolic signal(s) (n). (Note: argument is scanned once
when the trap is set and once when the trap is taken.)
Trap commands are executed in order of signal number or corresponding symbolic
names. Any attempt to set a trap on a signal that was ignored
on entry to the current shell is ineffective. An attempt to trap
on signal 11 (memory fault) produces an error. If argument is absent
all trap(s) n are reset to their original values. If argument is
the null string this signal is ignored by the shell and by
the commands it invokes. If n is 0 the command argument is executed
on exit from the shell. The trap command with no arguments prints
a list of commands associated with each signal number.

csh

onintr controls the action of the shell on interrupts. With no arguments,
onintr restores the default action of the shell on interrupts. (The shell
terminates shell scripts and returns to the terminal command input level). With the
- argument, the shell ignores all interrupts. With a label argument, the
shell executes a goto label when an interrupt is received or a child process
terminates because it was interrupted.

ksh

trap uses arg as a command to be read and executed when
the shell receives signal(s) sig. (Note that arg is scanned once when the
trap is set and once when the trap is taken.) Each sig
can be given as a number or as the name of the
signal. trap commands are executed in order of signal number. Any attempt to
set a trap on a signal that was ignored on entry to
the current shell is ineffective. If arg is omitted or is
-, then the trap(s) for each sig are reset to their original values.
If arg is the null (the empty string, e.g., "" )
string then this signal is ignored by the shell and by the commands
it invokes. If sig is ERR then arg will be executed
whenever a command has a non-zero exit status. If sig is DEBUG
then arg will be executed after each command. If sig is 0
or EXIT for a trap set outside any function then the command
arg is executed on exit from the shell. The trap command with
no arguments prints a list of commands associated with each signal number.

On this man page, ksh(1) commands that are preceded by one or
two * (asterisks) are treated specially in the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.

I/O redirections are processed after variable assignments.

Errors cause a script that contains them to abort.

Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.